ST. IGNACE, Mich. – The board overseeing the Mackinac Bridge announced Wednesday that its risk of collapse from a collision with a shipping vessel is lower than national thresholds, a new report found.
The bridge was one of 68 structures across 19 states that the National Transportation Safety Board (NTSB) recommended be evaluated for potential collapse risk after the deadly March 2024 collapse of the Francis Scott Key Bridge in Baltimore, caused by a collision with a container ship.
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In response to the recommendation, Mackinac Bridge Authority (MBA) members hired consultant engineering firm Parsons to evaluate the bridge against federally established guidelines.
Taking into account the bridge design and structural capacity, the characteristics of the Straits of Mackinac, and the size, type and frequency of vessels navigating near the bridge to calculate a “total annual frequency of collapse,” the report found that the Mackinac Bridge‘s collapse rate equated to .000097, or a return period of approximately 10,350 years — which is below the established limit of .0001 for critical bridges.
By comparison, the NTSB found that the Key Bridge was almost 30 times above the acceptable risk threshold for critical or essential bridges, according to the American Association of State Highway and Transportation Officials guidance.
The MBA reviewed the report during a closed session at the board’s regularly scheduled meeting on Wednesday. It was submitted to the NTSB in March, officials said.
“This report confirms what we’ve long believed to be true, that the risk of the Mackinac Bridge collapsing due to being struck by a vessel is extremely low,” said Bridge Director Kim Nowack in a news release. “We hope this gives greater assurance to everyone who crosses the bridge that there is very little danger of such a tragedy here.”